1. Field of the Invention
The present invention relates to an apparatus for controlling a gas turbine and a system with such an apparatus. More particularly, the present invention relates to a control apparatus for controlling combustion oscillations and a system with such a control apparatus.
2. Description of the Related Art
For a conventional gas turbine, flow rates of air and fuel respectively fed to a combustor are determined in advance based on the output power of an electric power generator, and temperature and humidity of ambient air, and the conventional gas turbine is operated by using the determined flow rates. However, there is a possibility that actual flow rates are different from those at the design of the gas turbine or those on test running, because of degradation of a compressor and clogging of a filter. At that time, the combustion stability can be reduced and combustion oscillations will be caused. The combustion oscillations seriously obstruct the operation of gas turbine. Therefore, it is strongly requested to minimize or eliminate the combustion oscillations from the viewpoint of the protection of plant facilities and the operation rate of the facilities. For this purpose, a control system of the gas turbine is adjusted by a skilled engineer several times a year in order to prevent the combustion oscillations and confirm and maintain the combustion stability. However, these works by turn raise the maintenance cost and reduce the operation rate of the gas turbine.
In conjunction with the above description, Japanese Laid Open Patent Application (JP-A-Heisei 9-269107) discloses an apparatus and method for suppressing combustion oscillations of a combustor. In this reference, the combustion oscillation suppressing apparatus is comprised of a combustion oscillation suppressing section. The combustion oscillation suppressing section has a frequency analyzer, a central processing unit, a power amplifier and a controller section. The frequency analyzer frequency-analyzes fluctuations of combustion gas pressure detected by a pressure sensor in the combustor, and the central processing unit achieves the oscillation stability of the combustor based on a frequency band of the pressure fluctuations detected by the frequency analyzer. The power amplifier amplifies an output signal of the central processing unit and the controller section controls a combustion valve by applying the amplified output signal as a valve switch signal. In the suppressing method pays attention to low frequency combustion oscillations. The frequency of combustion oscillations is predicted based on fuel to air ratio when the combustion oscillation has occurred. When a low frequency combustion oscillation has occurred, the fuel to air ratio is varied to suppress the occurrence of low frequency combustion oscillations. Because low frequency combustion oscillations can adversely affect the facility, the facility is protected against damages by suppressing low frequency combustion oscillations.